Cleaning systems for blanket cylinders of an offset web press are already known. In a known offset web press, a web is fed through a plurality of printing units, where images of different colors are printed onto the web. The web is then fed to a dryer, chill roll and a folder or other finishing equipment. The printing units each have an upper and lower blanket cylinder which define a nip through which the web passes. Each blanket cylinder has an associated plate cylinder having an ink feed.
A cleaning device, which includes a brush roller with bristles for selectively contacting the blanket, is associated with each blanket cylinder. Provided in the cleaning device is a cleaning fluid distribution tube for applying cleaning fluids, including organic solvents and water, to the brush roller.
During normal press operation, the brush roller is out of contact with the blanket and the cleaning device is inactive. Ink, gum, clay coatings, anti-offset powders and other substances may build up at this time on the blanket surface, which then needs to be cleaned.
When the press is to be cleaned during a cleaning or wash cycle, cleaning fluids are applied to the blanket and the brush roller contacts the blanket. The web is still running at this time, and much of the waste fluid, containing solvents, other fluids and waste particles from the blanket surface, is carried away by the web. The rest is collected by a drain tray.
Such a cleaning system is described in U.S. Pat. No. 5,109,770, which is hereby incorporated by reference.
However, when the width of the web is less than the width of the blanket, i.e. the web is not against its lateral limit on the blanket, significant amounts of ink build up between the lateral limit and the actual edge of the web during normal printing operation of the press.
The normal cleaning or wash cycle then is unable to sufficiently remove this excessive build-up of ink, leading to several problems, including smudging and friction at the edge of the web, which can lead to poor print quality and web breaks.